Molecular rearrangement of cycloalkadienic compounds



United States Patent 3,420,905 MOLECULAR REARRANGEMENT OF CYCLOALKADIENIC COMPOUNDS Edwin L. De Young, Chicago, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., :1 corporation of Delaware No Drawing. Filed Dec. 16, 1966, Ser. No. 602,127 US. Cl. 260-666 4 Claims Int. Cl. C07c 5/30; C07c 5/24 ABSTRACT OF THE DISCLOSURE Cycloalkadienic compounds will undergo molecular rearrangement to form divinyl-substituted cycloalkanes in the presence of certain catalytic compositions of matter such as an alumina which has been pretreated by heating at a temperature above about 350 C.

This invention relates to a process for effecting the molecular rearrangement of cycloalkadienic compounds. More particularly, the invention is concerned with a process for effecting the molecular rearrangement of cycloalkadienic compounds in the presence of certain catalytic compositions of matter hereinafter set forth in greater detail to prepare dialkenyl-substituted cycloalkanes.

With the increased use of engines which are liquid propelled, such as rocket engines of the type used for missiles or jet engines of the type used for propelling various types of aircraft, it is essential that the fuels for these engines possess various and sundry desired characteristics. For example, the fuels must perform certain functions in each of the essentially three principal functional parts of the rocket engines. These three parts of a typical rocket engine comprise the thrust chamber, the propellent feed system, and the control system. An ideal rocket fuel must, therefore, be able to function properly in each of the aforementioned parts; for example, the fuel must burn in a stable and eflicient manner in the thrust chamber, must burn to form completely gaseous products when a gas generator propellent expulsion system is employed, as well as being able to cool the thrust chamber, must lubricate the pump parts and must operate the control valve. In addition, fuels which are used to operate the jet engines on aircraft must have a low freezing point due to the extremely low temperatures at which jet aircraft operate in the upper atmosphere and at the same time must maintain low viscosity and pour points. Therefore, it is necessary to enhance jet fuels or rocket fuels, the two terms for purposes of this invention being used interchangeably and connoting the same fuel. In this respect, certain hydrocarbons of particular configuration have been found to possess the aforementioned desirable characteristics and therefore may be used as blending materials whereby jet fuels of improved characteristics may be obtained thereby.

It is known that the heat of combustion of hydrocarbons on the basis of volume tends to increase with increasing density, while the gravimetric heat value of particular hydrocarbons is influenced mainly by the hydrogen content of the molecule. For example, aromatic hydrocarbons have a low gravimetric heat of combustion due to the low hydrogen content of the molecule and, in addition, possess low thermal stability and poor burnability thereby rendering these hydrocarbons relatively unsuitable as fuels for rocket or jet engines. On the other hand, saturated hydrocarbons such as paraffins have a high gravimetric heat of combustion due to the high hydrogen content of the molecule. However certain of these paraffins are not usable as rocket or jet fuels, specific examples of these being normal parafiins which possess high freezing points in relation to the size of the molecule. As hereinbefore set forth, a low freezing point is a desirable characteristic of a jet or rocket fuel due to the low ambient temperatures in which these particular engines are operated. Another drawback to the use of the normal paraflins is that their volumetric heat of combustion is low due to the low density of the molecule. Yet another type of hydrocarbon which is unsuitable for use as this particular type of fuel comprises olefinic hydrocarbons, these compounds being unsuitable because of poor thermal stability.

A particularly suitable type of hydrocarbons which may be used as a jet or rocket fuel comprises cycloalkanes and particularly those which contain certain alkyl sub-- stituents thereon. These hydrocarbons possess gravimetric heats of combustion and burning characteristics which are close to those of normal paraffins. In addition to these desirable characteristics, the cycloalkanes also possess lower melting and freezing points than do the corresponding normal parafiins, as well as having a relatively high thermal stability. Furthermore, the higher density and specific heat of the cycloalkanes are more advantageous in that the greater density of the compounds allows a smaller volume of fuel to be pumped to the engine thereby consuming less fuel to furnish the energy for pumping. Therefore, in view of all of the rigid specifications hereinbefore set forth, the type of fuel which best meets all of the requirements Will include dialkyl-substituted, and particularly a compound such as 1,2-diethylcyclohexane. This compound has been found to possess the proper density, the proper volatility, the proper luminosity and a low melting point.

In view of the aforesaid need for jet fuels, it is an object of this invention to provide a process for the preparation of compounds which may be further processed to provide a finished product which is particularly utilizable as a component of jet fuels.

A particular object of this invention is to provide a process for the molecular rearrangement of cycloalkadienic compounds and particularly cycloalkadienic hydrocarbons in the presence of a specific type of catalytic composition of matter to prepare compounds useful as jet fuels.

In one aspect, an embodiment of this invention resides in a process for the molecular rearrangement of a cycloalkadienic compound which comprises contacting said compound with a catalyst comprising an alumina which has been calcined at a temperature above about 350 C. at molecular rearrangement conditions, and recovering the resultant dialkenyl-substituted cycloalkane.

A specific embodiment of this invention is found in a process for the molecular rearrangement of cyclodecadiene which comprises contacting said cyclodecadiene with a catalyst comprising anhydrous gamma-alumina which has been calcined at a temperature above about 350 C. for a period of about three hours at ambient temperature and atmospheric pressure, and recovering the resultant 1,2- divinylcyclohexane.

Other objects and embodiments will be found in the following further detailed description of this invention.

As hereinbefore set forth, the present invention is concerned with a process for the molecular rearrangement of cycloalkadienic compounds, and particularly cycloalkadienic hydrocarbons whereby the production of dialkenyl-substituted cycloalkanes is accomplished by the aforementioned molecular rearrangement. The dialkenylsubstituted cycloalkanes which are prepared according to the process of the present invention may then be subjected to hydrogenation by any means known in the art in the presence of a hydrogenation catalyst such as one containing a metal of Group VIII of the Periodic Table per se or composited on a solid support to prepare the corresponding dialkyl substituted cycloalkanes, the latter compounds, as hereinbefore set forth, being utilized as a component of a jet fuel. The aforementoned molecular rearrangement will be effected in the presence of certain catalytic compositions of matter at molecular rearrangement conditions. These molecular rearrangement conditions will include ambient temperatures and pressures which range from atmospheric up to about 50 atmospheres or more, said superatmospheric pressures being effected by charging an inert gas such as nitrogen to the vessel in which the molecular rearrangement is taking place.

It has now been discovered that certain types of catalysts will effect the molecular rearrangement of certain cycloalkadienic compounds while other catalysts similar in nature, will be ineffective to rearrange the molecule. Examples of catalysts which may be used to effect the process of this invention will include certain refractory oxides which have been pretreated prior to use thereof as catalysts. Especially effective catalysts will comprise certain types of refractory oxides and particularly aluminas which have undergone pretreatment consisting of calcination of the anyhdrous alumina prior to use as a catalyst for a period ranging from about 3 to about hours at temperatures above about 350 C. Particularly preferred aluminas will comprise those possessing a relatively high surface area such as from up to about 300 square meters per gram. Examples of these aluminas will comprise anhydrous gamma-alumina, anhydrous eta-alumina, and anhydrous theta-alumina. The aforementioned aluminas will catalyze the molecular rearrangement of certain cycloalkadienic compounds such as cyclodecadiene in a Cope type rearrangement. That the use of the catalysts of this type to effect the reaction was unexpected inasmuch as it is known in the prior art that the Cope molecular rearrangement reaction was usually effected in the absence of a catalyst while using realtively high reaction temperatures. The use of these high tempeartures which were ordinarily required to effect the rearrangement in many cases results in side reactions with a concurrent poor yield of the desired product. However, by utilizing ambient temperatures to effect the molecular rearrangement, it is possible to use less expensive equipment and in addition obtain relatively high yields of the desired product, thus obviating the necessity for using complicated separation equipment such as fractional distillation, etc. In addition it is also contemplated within the scope of this invention that other cycloalkadienic compounds such as cyclododecadiene, cyclotetradecadiene, etc., may also be treated in the presence of the aforementioned catalytic compositions of matter under different reaction conditions such as elevated temperatures to effect a molecular rearrangement, although not neecssarily with equivalent results.

As hereinbefore set forth, the catalyst comprising an anhydrous alumina such as gamma-alumina is pretreated prior to use thereof by being calcined at a temperature ranging from about 350 C. upward for a period of from about 3 to about 10 hours. Following the calcination, the catalyst is maintained under a blanket of inert gas such as nitrogen in order that no oxidation of the catalyst or hydration of the catalyst may occur through contact with air or moisture, it being preferable to effect the molecular rearrangement in an anhydous atmosphere.

As will be hereinafter set forth in greater detail in the examples, the molecular rearrangement can not be effected when utilizing similar types of catalysts, and especially aluminas which have been pretreated in a different manner or which are not anhydrous in nature. For example, of the alumina has been exposed to air or has been pretreated with an alkali substance such as a salt or hydroxide of potassium, sodium, lithium, etc., the molecular rearrangement of a cycloalkadienic hydrocarbon will not occur. Likewise, silica gel which may be used as a catalyst in any reactions where alumina may be used will also be ineffective as a molecular rearrangement catalyst.

The process of this invention may be effected in any suitable manner and may comprise either a batch or continuous type operation. For example, when a batch type operation is used, a quantity of the cycloalkadienic hydrocarbon which is to undergo molecular rearrangement is placed in an appropriate apparatus containing an anhydrous alumina which has been calcined under conditions hereinbefore set forth in greater detail. In addition, the reactor is maintained under a blanket of nitrogen so that air or moisture does not come in contact with the catalyst and the cycloalkadiene. After a predetermined residence time, during which the reactant and catalyst are maintained in intimate contact by means of agitation or stirring, the process is discontinued and the reaction product is recovered. The desired product which comprises a dialkenyl-substituted cycloalkane such as for example, divinylcyclohexane, is recovered from the unreacted starting materials, after being separated from the catalyst, by conventional means such as fractional distillation, crystallization, etc.

It is also contemplated within the scope of this invention that the present invention may be effected in a continuous manner of operation. Due to the physical characteristics of the catalytic composition of matter, a particularly effective type of operation comprises the fixed bed method in which the catalyst is disposed as a fixed bed in the reactor, while the hydrocarbon is passed over said catalyst in either an upward or downward flow, preferably at a relatively low liquid hourly space velocity in order that a sufficient amount of time may elapse during which the catalyst and the hydrocarbon are in contact with one another. The reactor is maintained at the proper operating conditions of temperature and pressure and after a predetermined residence time has elapsed, the reactor effluent is continuously withdrawn. The effluent is then subjected to separation means whereby the desired dialkenyl-substituted cycloalkane is separated from any unreacted starting material and/ or side products and recovered. The unreacted starting materials may then be recycled to form a portion of the feed stock. Other types of continuous manner of operation will include the moving bed type of operation in which the catalyst and the hydrocarbon pass either concurrently or countercurrently to each other and the slurry type of operation in which the catalyst is carried into the reactor as a slurry in the hydrocarbon charge.

The following examples are given to illustrate the process of the present invention which, however, are not intended to limit the generally broad scope of the present invention in strict accordance therewith.

EXAMPLE I This example will illustrate the necessity for the particular type of catalytic composition of matter which is required to effect the molecular rearrangement of a cycloalkadiene. A charge comprising 50 milliliters of a hydrocarbon containing 55.5% of 1,5-cyclodecadiene and 0.8% of 1,2-divinylcyclohexane was placed in an apparatus along with 50 cc. of a catalyst comprising an anhydrous gamma-alumina which had been calcined for three hours at a temperature of 350 C. prior to use and maintained under a nitrogen atmosphere. The apparatus was placed in a shaker under a nitrogen atmosphere of 1 atmosphere and was thereafter shaken for periods of 1, 17, and 48 hours. At the end of this time, the shaking was discontinued and the resultant product subjected to a gas-liquid chromatographic analysis. The results showed the molecular rearrangement of the cyclodecadiene to divinylcyclohexane in the following table:

EXAMPLE 11 TABLE II Percent Start 1 hr. 17 hrs. 48 hrs.

Divinylcyclohexane 0. 8 0. 5 0. 5 0. 4 Cyclodeeadiene 55. 5 65. 9 62. 7 53. 9

It will be noted that the analysis disclosed the fact that a molecular rearrangement did not occur at room temperature utilizing this type of catalyst.

EXAMPLE III In this example, an alumina, which has been lithiated prior to use by treatment with lithium nitrate in an amount so that about 0.5% lithium measured as the metal on the catalyst base, was used in an attempt to obtain molecular rearrangement of cyclodecadiene. In like manner, 50 cc. of the lithiated alumina catalyst and 50 cc. of a hydrocarbon charge similar to that set forth in Example I above Were shaken together for a period ranging from 1 to 48 hours. At the end of this time, the mixture was subjected to a gas-liquid chromatographic analysis, the results of said analysis are set forth in Table III below.

A similar experiment utilizing 50 cc. of silica gel with 50 cc. of this catalyst produced the results set forth in Table IV below:

TABLE IV Percent Start 1 hr. 17 hrs. 48 hrs.

Divinylcyclohexane 0. 8 0. 5 0. 6 0. 5 Cyclodecadiene 55. 5 66.7 70. 8 59. 2

It is, therefore, readily apparent from the above examples that the molecular rearrangement of cycloalkadienic hydrocarbons to form dialkenyl-substituted cycloalkanes may be readily effected at ambient temperature when utilizing a particular type of catalyst composition of matter, namely, anhydrous alumina such as gammaalumina which has been calcined at a temperature above about 350 C. for a period of time ranging from about 3 to about 8 hours or more, the other types of catalysts being ineffective to accomplish the desired molecular rearrangement.

EXAMPLE IV In this example, 50 cc. of cyclododecadiene are shaken with 50 cc. of an anhydrous gamma-alumina catalyst which has been calcined for a period of approximately three hours at a temperature of about 350 C. and thereafter maintained under a nitrogen blanket. Upon completion of the shaking period, which may range from 1 to about 48 hours or more, a gas-liquid chromatographic analysis of the product will disclose that a major portion of the cyclododecadiene has undergone molecular rearrangement to form 1,2-divinylcycl0octane.

I claim as my invention:

1. A process for the molecular rearrangement of a cycloalkadienic compound selected fom the group consisting of cyclodecadiene and cyclododecadiene which comprises contacting said compound with a catalyst consisting of an alumina which has been calcined at a temperature above about 350 C. at molecular rearrangement conditions which include ambient temperatures and pressures ranging from atmospheric to about 50 atmospheres, and recovering the resultant divinyl-substituted cycloalkane.

References Cited UNITED STATES PATENTS 6/1967 Perry 260-666 OTHER REFERENCES Un tech et al.: J. Amer. Chem. Soc., 87 pp. 4501-6, 1965 (Book in Technical Library).

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Assistant Examiner. 

